Unit 5P.5: Making electrical circuits

Transcription

1 Unit 5P.5: Making electrical circuits Electrical circuits Designing circuits to solve problems Good and bad conductors Enquiry Skills Observing Experimenting By the end of this unit you should : Construct simple circuits using bulbs, switches and cells. Know that electricity flows round a circuit from positive pole of the cell to the negative one. Test whether a material is a good conductor of electricity. Know the relationship between number of cells and the brightness of bulbs. 701

2 5.14.1, 5.14,2 Physical Science Exploring Circuits, what do you remember? Get a simple torch light and take it apart, it may look similar to this: D C A B Can you Remember what each part is and what it does? Part Name What does it do? A B C connector D What happens if you put the batteries in a different order? i.e 701

3 Making Electrical circuits Activity: Make an electric circuit Your teacher will organize the following materials for you: Batteries, connecting wires, light bulb, sticky tape. Steps: - Light up the bulb using the battery and the conducting wires. - Draw a simple sketch showing you plan to do this: Remove the battery and observe. What happens? Where are the wires connected on the batteries and the bulb? How can you get the bulb to go on and off? Each battery has two terminals that have two specific signs (+, - ). Observe your battery and identify these two signs. Label it below: 701

4 - Indicate the location of these signs on the sketch you drew. -Represent in your drawing the flow of current. -What happens if you connect the two wires to the same terminal? Simple electric circuit If you succeeded in lighting up the bulb in the previous activity, then congratulations!! You just created a simple electric circuit. An electric circuit provides a complete, closed path through which the electric current flows. 770

5 -What can you add to this circuit to make it easier to put the light on and off? Here are some different types. 777

6 -Label the parts of a simple electric circuit above, use the following words: Battery Bulb Switch Wire a. What happens if one of these parts is not functioning? b. What happens when the switch is open? c. What do you think would happen if you added 2 more batteries!? 771

7 Key Questions 1.a. The drawing below shows the parts of a torch. Ahmed closed the switch. Why did this turn on the torch? b. The drawings below show two other torches. In both torches, the bulbs will not light even when Najib closes the switches. Look carefully at the drawings. i. Why is the circuit of torch A not complete? ii. What could you do to torch B to get the bulb to light?

8 2. Look at each diagram and explain why the bulbs will not light up. 771

9 Physical Science Types of electric circuit When using more than one light bulb in a circuit, the light bulbs may be connected in series (one after another) - in ONE LOOP. Activity: Series Circuit You will need: - Battery (4.5 V) -Two light bulbs (3-4.5 V) -connecting wires -switch Steps: - Set up the electric circuit as shown using all materials mentioned above. - Close the circuit by using the switch. - Remove one of the two light bulbs. What happens? Series circuit: A circuit that connects several bulbs one after another so that the current flows in a single path. Activity: Parallel circuit 771

10 You will need: The same materials used in the previous activity. Steps: -Set up the electric circuit as shown. -Remove one of the two light bulbs. What happens? Parallel circuit: a circuit that connects several bulbs in a way that the current for each bulb has its own path. (on separate branches). Key Words: Series electric circuit Parallel electric circuit Key Ideas: Using more than one light bulb in circuit give us series or parallel circuit. 771

11 2. Mark out the incorrect word in each of the following sentences. a) Two identical bulbs in a series circuit light together and go out together/ light together but go out separately. b) If one element in a parallel connection breaks down, all other elements will continue to function/ will stop functioning. c) The same current/ different currents pass( es) through two bulbs connected in series. 3. In this circuit, one bulb is unscrewed. (Taken out) Will the other bulb glow? Explain your answer Will the other bulb continue to glow?

12 Physical Science Bulbs Brightness Activity: What affects bulbs brightness? You will need: - 3 Batteries (4.5 V) -Light bulb (4.5 V) -Connecting wires Steps: -Try to light on 4.5 V light bulb using one 4.5V battery. -Repeat the previous steps using two 4.5V battery then 3 batteries. -Write down your observation for each trial. Trial 1 Trial 2 Trial 3 Do you know now what affects the bulb brightness? How did you know? 771

13 Demonstrating a bulb burning out Add a fourth battery to the last circuit you created. What did you observe now? Increasing the number of cells (battery) in series in a circuit will make bulbs shine brighter. Be Increasing careful the number of bulbs in series in the circuit Avoid situations where too much current passes through a makes bulbs shine less brightly. bulb, the bulb will burn out. This can be dangerous! Key Words: Brightness Key Ideas Decreasing the number of cells (battery) in series in a circuit will make bulbs shine brighter. Increasing the number of bulbs in series in the circuit makes bulbs shine less brightly. 771

14 Key Question Q1: Which of the circuits below give more light than the circuit on the right? Prediction: Result: 1- In which circuit will the bulb be brightest? 2-In which circuit will the bulb be the dimmest? b- Why do you think this is? Explain your answer

15 Designing circuits to solve problems Project Work in group, to design and make circuits of your choice that solve a problem. These may be circuits, that model real situations (e.g. the light in a room) or they may be circuits that perform a real function (e.g. light up a bulb when someone steps on a mat, or ring a bell when a door opens) Good and bad conductors. Material around can be divided into two groups according to whether they allow the passage of the electric current or not. Conductors include substances that allow the passage of the electric current (Metals), while insulators include substances that do not allow the passage of the electric current. Conductors: Substance that allow the passage of the electric current (Metals). 717

16 Insulators: Substance that Do Not allow the passage of the electric current (Non-Metals). Activity: Classifying substances into conductors and insulators. You will need: Battery, light bulb, connecting wires, different kinds of materials (paper, aluminum foil, plastic ruler, pencil, wood, glass, copper wire, nail). Procedure: -Build a circuit similiar to that shown. Connect the material that you want to test here. E.g 711

17 -Connect one of the suggested substances as an additional part to the electric circuit you built. Check if the light bulb is still on. i.e. testing a nail/screw -Repeat the same step by using the other materials. -Sort the substances as Conductors or insulators in the table below. Conductors Insulators What electrical appliances are made of? Look at the following electrical appliances: Radio Kettle Flash light Iron 711

18 Complete the table for each and explain why certain parts are conductors and other parts insulators. Object Conductor Insulator parts Why? parts Why? Iron Kettle Radio Flash light 711

19 Key Words: Conductor Insulator Key idea Substances can be divided into two groups according to whether they allow the passage of the electric current or not. (Conductors or Insulators). Key Question Put a tick ( ) in the box if you think the bulbs will light up. 711

20 2. a- Make a table with two columns. The first should have the heading conductors and the second, insulators. Put the following materials in the correct column in the table below. Wool Glass Coin Pencil Plastic pen beaker eraser Nail Wooden Drawing Key ruler pin Insulators Conductors b- How would you summarize what sort of materials are conductors and which are insulators? Conductors Insulators 711